Expanding fastener



C. A. TAYLOR ET AL EXPANDING FASTENER Jan. 16, 1951 Filed Aug. 10, 1945k EHWIAVNE Patented Jan. 16, 1951 EXPANDING FASTENEB Cecil Arthur Taylorand Harold Hibbert, London, England, assignors to The Rawlplcg CompanyLimited, London, England, a British company Application August 10, 1945,Serial No. 610,094 In Great Britain August 17, 1944 6 Claims.

This invention relates to improvements in fastening devices intended foruse in securing fittings or articles such as hooks, switches, cabiinets,etc, to walls constructed of materials such as plaster-board,composition board, hollow tiles, and the like, where the availablethickness of wall to receive a fastening device is not sufficient toenable efficient or satisfactory fixing to be made by conventionalmethods such as the known metal or fibrous plugs, which depend upon thefriction between the plug and the cylindrical wall of the hole in whichit is inserted.

A collapsible tubular fastening device of the type comprising aninternally threaded substan tially cylindrical end member adapted to beengaged by a screw-threaded member passing through the device, and apair of oppositely disposed deformable strips adapted to extend througha wall having a preformed hole, the free ends of said strips beingenlarged and transversely curved whereby a substantially cylindricalhead memberis formed for placement in said preformed hole, is known. Ithas been found in practice that when collapsible fastening devices ofthis type are used, the tightening of an externally screw-threadedmember in the internally screw-threaded end member causes a torque to betransmitted between these members so as to tend to twist the said endmember in the same direction as the screw or bolt is being twisted inorder to draw the said end member towards it and effect the desiredcollapse of the side strips. This torque, often of considerablemagnitude, stresses the side strips in transverse bending. Due to theirrelative structuralweakness it has been found in practice that theseside members often yield under this transverse bending stress beforethey yield in compression so that the screw or bolt drags the end memberaround with it before the collapse occurs. In many cases the sidemembers may become so twisted and entwined that the desired collapse isentirely prevented.

It is the object of the present invention to overcome this difficultyand accordingly the invention comprises a device of the type describedwherein the deformable strips are inclined with respect to thelongitudinal axis of the tubular fastening device, in such a manner thatthe free ends of the deformable strips are pre-formed so as to berotationally displaced about said axis with respect to the ends of thestrips attached to the end member of the device, such rotationaldisplacement of the free ends being in the same sense as the sense of,rotation of the screwthreaded member during the insertion thereof intothe end member.

It will be seen that, under these conditions, the threaded end memberwill tend to be rotated by an inserted screw in a direction such as tostress the side strips partly in transverse bending as before and partlyin compression, the proportion between these two stresses beingadjustable at will by the angle of inclination imparted to the stripsduring the manufacture of the device. In this way, much of the torque isprevented from bending the strips transversely, and furthermore, saidtorque is usefully employed stressing the strips in compression and inassisting the longitudinal pulling force exerted on the end member tobring about its collapse in the desired manner.

Various views of a device according to the invention are shown by way ofexample in the accompanying drawing, in which Figure l is a View of adevice according to the invention prior to its insertion in a previouslyprepared hole in a thin wall or the like.

Figure 2 is a side view at right angles to that shown in Figure 1,

Figure 3 is a side view similar to Figure 2, showing the device in theposition it assumes in a previously prepared hole, prior to collapse,

Figure 4 shows the blank strip from which the device of Figures 1 to 3is made.

Figure 5 is a sectional view of the device shown ,in Figures 1 to 3,after it has collapsed, in position extending through a wall panel orlike fix- --ture,

' punched to form a substantially cylindrical end member I having acentral screw-threaded bore in a smaller cylindrical extension 2, twooppositely disposed side strips 3 and at the end of such strips 3,enlarged portions 6 bent each to form a semicylindrical head member. Theside strips 3 are arranged so that when the device is ready for use,

as shown in Figures 1 to 3, they are inclined with respect to thelongitudinal axis of the device, in such a manner that the enlargedportions 4 are P, rotationally displaced about said axis with respect tothe ends of the strips attached to the end member I, such displacementof the enlarged portions 4 being in the same sense as the sense ofrotation of a screw or like member during the insertion thereof into theend member. The device is then inserted into a previously formed holeextending through a wall or the like 6 (see Figure until the end Ithereof having the central screw-threaded part 2 projects beyond thefurther face of the wall or the like. A screw 1 is then inserted throughthe hole in the article being fixed or a washer may be substituted forthe latter if it is desired that the device be collapsed as a separateoperation previous to the final fixing, by which method a shorter screwmay be used for making the fixture than that which is necessary for thepreliminary collapsing operation. On tightening up the screw, the head4, 4 is drawn up against the back of the article being fixed (or thewasher as the case may beland further tightening draws the screw end 2towards the head of the screw and forces the side strips 3 to buckleoutwardly under the longitudinal pressure thus applied thereto. Theparts of the side strips 3 projecting inwardly beyond the hole are thusforced outwards and fold up to form radially projecting abutments 5 onthe inner end of the device, the withdrawal of which through the hole isthus positively prevented. The article 8 to be fixed upon the wall isheld in position by the engagement of the screw I in the end 2 of thecollapsed device.

In order further to facilitate ready collapsing or deformation of thedevice, the strips 3 may be provided with oppositely arrangedindentations or corrugations as indicated at 9 in Figure 6, these beingstamped in the strips when blanking out or during the course of thesubsequent pressing operation. The object of these indentations 9 is notto arrange for collapse at any particular point but to initiate theoutward buckling, the actual points of fold in the side strips beingdetermined by the length of the side strips projecting through the holeand, therefore, capable of deformation. A plurality of such indentationsa may, if desired, be arranged in each strip 3. Further to facilitatecollapsing of the side strips 3, the latter may in the course ofmanufacture be given a slight outward set as shown in Figures 1 and 2,the resiliency 'of the metal causing such strips 3 to be slightlyoutwardly curved, as shown in Figure 3, when the members 4, 4 arebrought together by the insertion of the device into its hole.

In order to ensure that after collapse of the device a substantial areaof the outer surface of each strip 3 shall lie in contact with the innerface of the Wall through which the device has been passed, the saidstrips are advantageously so formed that longitudinal pressure thereoncauses outward buckling of each strip to be initiated at a point in thelength thereof projecting inwardly beyond the inner face of the hole inthe wall board or the like which is nearer to the wall than to thescrewed end 2 of the device.

In order so to predetermine the point at which such outward bucklingshall be initiated, the nicks or indentations 9 therein maybe suitablypositioned, or alternatively the strips may be of tapering width, i. e.the width of each strip may be increased towards the screwed end of thesocket (not shown), the inner end of each strip thus being relativelymore strongly resistant to 4 collapse than the part thereof closer tothe inner face of the wall.

Thus, when longitudinal pressure is exerted upon the device, the strips3 collapse at a point I! substantially one third of the inwardlyprojecting .length thereof beyond the wall 5, as shown in Figure 5a, thepart I8 thereof adjacent to the wall is caused to lie closelythereagainst.

' In order to prevent rotation of the device in its hole when beingcollapsed or deformed, or after such collapsing or deformation, ribs,tongues or projections IIi may extend laterally from the head members 4,4 as shown in Figures 1 to 6, such projections biting into the sides ofthe hole in the wall and positively preventing rotation of the devicetherein.

The form of device according to the invention shown in Figure 7 isespecially suitable for use with thin cardboard or metal. Instead of thehead member being provided with projections to prevent rotation, thesaid head member II is made hexagonal in shape so that, when driven intoa circular hole of approximately the same diameter as the distanceacross the flats of the hexagon, the head member I I of the device I5becomes firmly fixed against rotation. Nicks or indentations I3 may beprovided in the arms I8 of the device in order to facilitate initiationof the collapse of such arms IS. The device is further provided withbent over lugs I2 as shown in Figure 7, to form a partial flange,partly'to prevent the device I5 being pushed right through the apertureand partly to provide an adequate surface to bear against the back ofthe article being fixed when the screw is being tightened. In this formof device, the diameter of the bore formed in the end M thereof ispreferably such that the external diameter of the screw is only slightlyless than the internal diameter of the device, so that when the sidestrips It thereof are collapsed to form radial abutments on the innerface of the walls, since each such abutment comprises two thicknesses ofmetal (in a manner similar to that shown in Figure 5) the force requiredto destroy the fixing by forcible withdrawal of the screw is equaleither to the strength of the screw itself or to the strength of thematerial of the wall or the like through a hole in which the device hasbeen inserted. Since the inner collapsed portion of the device comprisestwo thicknesses of the strip from which it is made, and the spacebetween the internal wall of the prepared hole in the wall or the likeand the exterior of the screw is substantially only a single thicknessof such strip, it will be appreciated that to withdraw the collapsedportion of the device through the prepared hole would be impossiblewithout destruction either of the screw or of the wall itself.

We claim:

1. An expanding fastener comprising an internally threaded,substantially cylindrical end member adapted to be engaged by ascrewthreaded member passing through the device, and a pair ofoppositely disposed deformable strips adapted to extend through a wallhaving 'a pre-formed hole, each of said strips being formedintegrally-at one end with said end member and having its other endfree, the free ends of said strips being enlarged and transverselycurved so that, when said curved and enlarged end portions are broughttogether, a substantially cylindrical head member is formed for place--ment in said preformed hole, the deformable strips being inclined withrespect to the longitudinal axis of the fastener in such a manner thatthe free ends of the deformable strips are disposed in positionsrotationally displaced about said axis relatively to the ends of thestrips attached to the end members of the device, such rotationallydisplaced relative positions of the said free ends being in the samesense as the sense of forward rotation of the screw-threaded member tobe inserted into the end member.

2. An expanding fastener in accordance with claim 1, wherein thecorresponding ends of. the deformable strips are diagonally oppositelydisposed with respect to each other.

3. An expanding fastener in accordance with claim 1, wherein each ofsaid enlarged and curved end portions is provided at one edge with alateral projection for engagement with the surface of the preformed holeto prevent rotation of the head member.

4. An expanding fastener in accordance with claim 1, wherein eachdeformable strip is formed with at least one transverse corrugation inorder to facilitate collapse or deformation thereof at a desired pointin its length.

5. 'An expanding fastener in accordance with claim 1, wherein eachdeformable strip is bent slightly outwardly in the form of a bow inorder to facilitate collapse or deformation thereof.

5. An expanding fastener in accordance with claim 1, wherein thefastener is composed of a unitary piece of sheet metal.

. CECIL ARTHUR TAYLOR.

HAROLD HIBBERT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

